International Business Machines Corporation

John Michael Kaiser, Deceased

Ravi Kumar Arimilli

Derek E Williams

Warren Edward Maule

Raymond J Eberhard

Vincent P Zeyak, Jr

Eddie Wong

A method and apparatus for preventing the occurrence of deadlocks from the execution of unresolvable system bus operations. In general, each snooper speculatively accepts a given operation when it has a snoop buffer available. However, rather than unconditionally processing the operation, the snooper waits to determine if another participant retried the operation due to unavailability of a snoop buffer. If some snooping participant retrys an operation, all snoopers that speculatively accepted an operation for processing abandon said operation. If no snooping participant retrys the operation, sufficient snooping resources were available for all necessary caches to begin processing the operation and the initiator can consider the operation completed. In other words, no operation is processed until all the necessary snooping resources are available to accept the operation. This prevents the system from getting into the ping-pong deadlock. Snoopers can safely assume that each presentation of an operation must be propagated and that no operation will have been fully or partially processed by some other snooper. The operation cannot proceed until all of the available resources are available and once available, the operation is propagated only once by those snooping resources.

Method and apparatus for executing self-snooped unresolvable system bus

A method and apparatus for preventing the occurrence of deadlocks from the execution of multiply-initiated multiply-sourced variable delay system bus operations. In general, each snooper excepts a given operation at the same time according to an agreed upon condition. In other words, the snooper in a given cache can accept an operation and begin working on it even while retrying the operation. Furthermore, none of the active snoopers release an operation until all the active snoopers are done with the operation. In other words, execution of a given operation is started by the snoopers at the same time and finished by each of the snoopers at the same time. This prevents the ping-pong deadlock by keeping any one cache from finishing the operation before any of the others.

Method and apparatus for executing multiply-initiated, multiply-sourced

System and method reading data from storage by speculatively accessing storage and overlapping data bus access with status determination, thereby reducing storage read access latency. Also, a system and method is provided for reducing storage read access latency by accessing a data bus substantially simultaneously with availability of data from storage. Upon receipt of a storage read request, and before status determination, the requested data is read from storage. Optionally, depending upon bus architecture or the need to minimize control circuitry, control of the data bus may speculatively be sought so that data may be loaded to the data bus upon availability from main storage, still whether or not status has been resolved. Subsequently, if status cancels the read request, further data bus loading is terminated.

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Cedar Park, TX, United States of America

John Michael Kaiser, Deceased